The present invention relates to the manufacture of foam-in-place cushions having a foam-forming composition contained within a flexible bag formed from polymer film supplied as continuous web material, the polymer film being sealed along longitudinal and transverse seals to contain the foam-forming composition, and being severed to detach a foam-in-place cushion from the remaining web material.
Foam-in-place packaging is a highly useful technique for on-demand protection of packaged objects. In its most basic form, foam-in-place packaging comprises injecting a foam-forming composition from a dispenser into a container that holds an object to be cushioned. Typically, the object is wrapped in plastic to keep it from direct contact with the rising (expanding) foam. As the foam rises, it expands into the void space between the object and its container (e.g., a corrugated board box), thus forming a custom cushion for the object.
A common foam-forming composition is formed by mixing an isocyanate compound with a hydroxyl-containing material, such as a polyol (i.e., a compound that contains multiple hydroxyl groups), typically in the presence of water and a catalyst. The isocyanate and polyol precursors react to form polyurethane. At the same time, the water reacts with the isocyanate compound to produce carbon dioxide. The carbon dioxide causes the polyurethane to expand into a foamed cellular structure, i.e., a polyurethane foam, which serves to protect the packaged object.
In other types of foam-in-place packaging, an automated apparatus produces foam-in-place cushions by making bags from flexible plastic film and dispensing a foam-forming composition into the bags as they are being formed. As the composition expands into a foam within a bag, the bag is sealed shut and typically is then dropped into a container holding the object to be cushioned. The rising foam again tends to expand into the available space, but does so inside the bag. Because the bags are formed of flexible plastic, they form individual custom foam cushions around the packaged objects. Exemplary types of such packaging apparatus are assigned to the assignee of the present application, and are illustrated, for example, in U.S. Pat. Nos. 4,800,708, 4,854,109, 5,027,583, 5,376,219, and 6,003,288, the contents of each of which are incorporated entirely herein by reference.
As will be noted from the patents listed above, the typical method of forming a foam-in-place cushion from a plastic bag is to heat-seal plies of plastic film material together both transversely and longitudinally as they are being fed from a stock supply to form a generally rectangular bag with the foam inside. In some cases, the stock supply of plastic film material can comprise a C-folded web so that one side of the bag is a fold rather than a heat seal. Foam-in-place packaging apparatus that operate in accordance with such methods have gained rapid and wide acceptance in the marketplace and have served their purposes well.
However, improvement in the operation of such apparatus is continually sought. In this regard, one difficulty associated with conventionally produced foam-in-place cushions is that the cushion as it is discharged from the apparatus does not have the foam-forming composition evenly distributed in the cushion. The foam-forming composition tends to be dispensed into the bottom of the bag and immediately begins expanding as the precursor chemicals react. It is a common practice for an operator to take the cushion discharged from the apparatus, lay the cushion on a flat surface, and use his or her hands to redistribute the foam-forming composition within the cushion into a layer of generally uniform thickness before the cushion is placed into a shipping container.
The problem with this technique is that by the time the operator is able to get the cushion onto the flat surface, the foam-forming composition has already undergone a substantial degree of expansion. When the already-formed foam is redistributed, the cellular structure of the foam is disturbed. This can cause the cushion to expand in volume by a lesser amount than it was designed to do, and therefore the foam density is higher than desired. Moreover, the uniformity of the foam density may be compromised, such that substantial non-uniformities of density may be created in the cushion. Consequently, the cushion may not have the protective properties it was designed to have.